A U.S. defense contractor killed in a blast in Bulgaria last week was working for a program to train and equip Syrian rebels fighting against Islamic State, U.S. officials said Wednesday.

The American died when a rocket-propelled grenade misfired at a military range in Anevo in central Bulgaria on Saturday. 

The U.N.'s peace envoy for Syria Staffan de Mistura has extended wide-ranging talks in Geneva by another month until July, his spokeswoman said Wednesday.

Jessy Chahine said the talks, launched on May 5 to allow separate consultations with regional and domestic players in the hope of reviving stalled dialogue on the conflict, would continue next month.

More than 2,000 refugees crossed from Syria into Turkey on Wednesday, fleeing clashes pitting Kurdish fighters against the Islamic State (IS) group, a Turkish official said.

"Of those displaced, 686 are Iraqi nationals who first fled their country and then were forced to flee Syria," a Turkish official told AFP.

The U.S.-led coalition carrying out air strikes against the Islamic State group needs to target the jihadists' command centers, but this is easier said than done, French army chief Denis Mercier said Wednesday.

He compared operations in Iraq, where French warplanes are carrying out air strikes, and Syria, where the U.S. is bombing jihadist positions, to the 2011 international intervention in Libya.

Jihadists from the Islamic State group blew up a pipeline feeding natural gas from eastern Syria to the suburbs of the capital Damascus early Wednesday morning, a monitor said.

The Syrian Observatory for Human Rights said IS blew up the pipeline near the T-4 military airport in the east of central Homs province shortly after midnight.

Iran on Wednesday insisted it has not deployed troops in Syria to strengthen regime forces, denying reports that thousands of foreign fighters have been flown in to help defend Damascus.

Reports on "the military presence of countries friendly to Syria" are "unfounded", foreign ministry spokeswoman Marzieh Afkham said at her weekly press briefing.

Lebanese Forces leader Samir Geagea has said that the dialogue between his party and the Free Patriotic Movement should have started a long time ago.

“But it's better late than never,” Geagea said in an interview to be published on Thursday, according to his press office.

Barack Obama's admission that he has an incomplete strategy to combat the Islamic State group is politically toxic, but history shows many of his predecessors also decided that "muddling through" a crisis was the least-worst option.

They were seven small words that did not help the 44th president one little bit after a G7 meeting in the clean air of the Bavarian Alps: "We don't yet have a complete strategy."

The agency in charge of U.S. transportation security came under renewed fire Tuesday as a report revealed that American airports had hired dozens of people with terror links.

The Transportation Security Agency is already reeling after a recent Department of Homeland Security report found that investigators could sneak fake bombs and weaponry through security with a 95 percent success rate.

A U.S. commando raid in Syria last month that killed a senior figure from the Islamic State group produced a wealth of information about the jihadists' finances and leadership, the New York Times reported Tuesday, citing U.S. officials.

Material seized in the May 16 raid against Abu Sayyaf, believed to be the group's top financier, already helped U.S. forces track down and bomb another IS leader in eastern Syria on May 31, unnamed officials told the Times.